Turbines, including gas or steam turbines, include nozzle assemblies that direct a flow of steam or gas into rotating blades, or airfoils, that are coupled to a rotating shaft so as to cause the rotating shaft to turn. One configuration for the nozzle assemblies includes a singlet design, including a blade, or airfoil, between inner and outer sidewalls, with the sidewalls coupled to an inner and outer ring, respectively, and with mechanical axial and radial stops at the interfaces between the sidewalls and rings.
Fabricating the singlet nozzle assemblies requires welding the various parts of nozzle assembly together on both sides of the nozzle, i.e., welding the inner end of the nozzle to an inner ring, and welding the outer end of the nozzle to an outer ring. Typically, both an entrance and exit side of the interface between a nozzles and a ring are welded together. However, welding can introduce large amounts of heat that can distort the parts of the singlet nozzle being welded. One concern of the designs that use weld on entrance and exit sides is the cost of having to flip the part to do the opposite side weld. Another issue is the added distortion of having to weld on both the entrance and exit side of the nozzle assembly. In other words, lifting can occur when welding the first side of the nozzle to the ring because the opposite side will lift off the ring due to weld shrinkage on the welded side.
Another issue with welding both the entrance and exit sides of the interface between an airfoil and a ring is that after welding, a significant amount of material would need to be removed from the nozzle assembly to create an inner and outer sidewall leading up to the airfoil.